Method and apparatus for producing zeolite

ABSTRACT

A composition comprising an incineration ash or an aluminosilicate as a raw material is added with an aqueous alkaline solution from an alkali storage tank ( 3 ) and heated. The resultant pre-mixture is then mixed and kneaded by a kneader ( 4 ) to prepare a kneaded mixture ( 19 ) in the form of a slurry or mud. The kneaded mixture ( 19 ) is moved continuously and irradiated directly with an electromagnetic wave of 300 MHz to 30 GHz in an electromagnetic wave irradiation unit ( 21 ), to thereby convert it to zeolite. The zeolite thus formed is cleaned by means of a cleaning machine ( 7 ) and dried with a rotary steam dryer ( 9 ). This method can be employed for producing an artificial zeolite with a reduced amount of alkali used and discharged, at a lower energy expenditure, and a reduced time for production.

TECHNICAL FIELD

The present invention relates to a technology for producing zeolite fromincineration ash or a composition containing aluminosilicate as a rawmaterial.

BACKGROUND ART

Conventionally, fly ash generated in the course of coal burning and acomposition containing aluminosilicate have been used as raw materialsfor producing artificial zeolite. Japanese Unexamined Patent PublicationNo. 6-321525 and No. 6-321526 disclose methods and apparatuses forproducing zeolite from such raw materials by means of a hot aqueousalkaline solution.

Japanese Unexamined Patent Publication No. 10-324518 discloses a methodof continuously producing artificial zeolite by a circulatingfluidized-bed as well as a device therefor.

In the conventional methods of producing artificial zeolite, a mixtureformed by mixing fly ash or a composition containing aluminosilicatewith an alkali is heated by radiation heat or conduction heat. Thethermal energy density has limits to increase, which often makes aheating time longer. Further, the reaction speed of forming zeolite witha hot aqueous alkaline solution is slow, thereby taking a longer time toproduce artificial zeolite. In other words, heating is performed fromoutside of particles, and therefore a longer time is needed for heatinflux into the particles and for diffusion of an alkali, resulting in alonger reaction time as a whole.

In addition, the zeolite generated by the thermal alkaline reactionforms crust over the particle surface, retarding the reaction inside theparticles. Thus, the formation of zeolite is hindered, and the zeoliteconversion rate is not high.

Furthermore, in the conventional methods, a large amount of sodiumhydroxide which is not involved in the reaction requires a large amountof work and time in recovering and reutilizing the alkali, making itdifficult to produce artificial zeolite having a high function at a lowcost.

There is a further problem from a viewpoint of energy saving since theconventional methods require the steps of separating artificial zeolitefrom an alkaline solution, and washing and drying the zeolite, and theseparating and drying steps need a large amount of energy, resulting ina high production cost.

An object of the present invention is to provide a technology whichenables production of artificial zeolite by a simpler process, comparedwith the conventional technology, with a reduced amount of alkali usedand discharged at a lower energy expenditure, and a reduced time forproduction.

DISCLOSURE OF INVENTION

In order to solve the above-described problems, the method for producingzeolite according to the present invention comprises adding an aqueousalkaline solution to incineration ash or a composition containingaluminosilicate to prepare a mixture in the form of slurry or mud,heating the mixture, and directly irradiating the mixture withelectromagnetic waves having frequencies ranging from 300 MHz to 30 GHz,while continuously moving the mixture, to form the zeolite. By employingthis process, an alkali in a minimum amount necessary for the reactionpenetrates into the particle solid phase of incineration ash or thelike, and the alkali instantly forms zeolite by means of the heatgenerated from inside the particles by the electromagnetic waveirradiation. This process, therefore, enables the production ofartificial zeolite in a short time, with a reduced amount of alkali usedand discharged. Further, the conventional solid-liquidseparation/purification processes are not necessary, thereby simplifyingthe whole process.

It is noted that incineration ash or a composition containingaluminosilicate may include natural zeolite and artificial zeoliteproduced by other production methods which have not been converted intophillipsite. Accordingly, the present invention can be applied toimproving the properties of natural or other zeolite.

Since the electromagnetic wave irradiation causes heat generation onlyin the mixture of incineration ash or the like, virtually withoutheating the surrounding devices, the atmospheric gases, etc., the heatefficiency is high and the energy expenditure can be lowered.Furthermore, the electromagnetic wave is irradiated after the mixture isheated, thereby raising the heat conversion efficiency to approximately70%. As this preliminary heating process, the mixture is preferablyheated at a temperature ranging from 80 to 150° C.

The principal component of the zeolite produced according to the presentinvention is phillipsite. It may also include faujasite, zeolite A,hydroxy sodalite, etc. with non-zeolite components, that is, componentsother than zeolites, such as unburned carbon, iron, etc.

It is noted that the incineration ash described in the present inventionis incineration ash made of compositions containing aluminosilicate. Theincineration ash includes coal ash, incineration ash of sludge generatedin paper manufacturing, incineration ash from activated sludge producedby sewage disposal, incineration ash from city garbage, incineration ashof solidified fuel made from garbage or the like. The compositioncontaining aluminosilicate refers to a mineral containing a salt formedby partially substituting silicate or silicon dioxide with aluminum.Such mineral is exemplified as orthoclase, anorthite, analcime,chabazite and mica.

By irradiating the electromagnetic waves having frequencies ranging from300 MHz to 30 GHz, the dipole moments of water molecules existing in themixture of incineration ash or a composition containing aluminosilicateand an aqueous alkaline solution vibrate vigorously (from severalhundred million to several billion times per second) to give a hightemperature by generating heat inside the particles of incineration ashor the like, which promotes a hot alkaline reaction instantly. Thus, thereaction to form zeolite, which took several hours to several tens ofhours according to the conventional methods, can be completed in severalminutes.

Since the mixture of incineration ash or a composition containingaluminosilicate and an aqueous alkaline solution is in the form ofslurry or mud, the handling and transportation efficiency in theproduction process are improved. Further, an efficient heat generationcan be realized by the electromagnetic wave irradiation. Thus, theamount of alkali can be adjusted to a minimum necessary for thereaction, resulting in great reduction of the amount of discharged wastealkali.

The reaction to form zeolite nuclei which determines the rate of overallreaction to form zeolite is accelerated by adding particles for nucleusformation in advance to incineration ash or a composition containingaluminosilicate. Thus, the reaction speed of forming, zeolite is raisedby three to five times, thereby producing artificial zeolite in ashorter time. As the particles for nucleus formation, zeolite particles,glass powder, etc. are suitable.

Since a mixture of incineration ash or a composition containingaluminosilicate and an aqueous alkaline solution is continuously movedduring irradiation of electromagnetic waves, the control and adjustmentof the irradiation conditions are easier, allowing continuous working ofthe overall process for producing zeolite. Accordingly, the efficiencyof the process is enhanced. It is noted that, if the mixture ofincineration ash or the like has edges or protrusions, the electricfield tends to concentrate on the edges or protrusions, causing unevenheating. It is preferable to employ a cylindrical rotary heater or aconveyor-type heater which can move the heating surface up and down toprevent such uneven heating.

By using, as incineration ash, fly ash formed in the course of coalburning or garbage incineration, industrial wastes can be converted intouseful resources. Fly ash formed in the course of coal burning refers tominute ash particles collected by a dust collector in the course of coalburning using a pulverized coal-fired boiler. The ash particles includesilicon oxide, aluminum oxide, calcium oxide, etc., with an ignitionloss of 5% or less and a specific gravity of 1.9 or more, having aparticle size distribution passing 75% or more of the particles througha 44 μm standard sieve. Fly ash generated by garbage incineration has acomposition containing silica, alumina and lime, which is similar to thefly ash generated by coal burning.

The apparatus for producing zeolite according to the present inventionis an apparatus comprising: kneading means for adding an aqueousalkaline solution to incineration ash or a composition containingaluminosilicate to form a mixture and for kneading the mixture; heatingmeans for heating the mixture kneaded by the kneading means;electromagnetic wave irradiation means for irradiating the heatedmixture with electromagnetic waves to form zeolite; cleaning means forcleaning the zeolite formed by the electromagnetic wave irradiation; anddrying means for drying the cleaned zeolite.

The apparatus having the above construction realizes a simpler processfor producing artificial zeolite, compared with the conventionaltechnology, with a reduced amount of alkali used and discharged, at alower energy expenditure, and a reduced time for production.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a process in an apparatus forproducing zeolite. FIG. 2 is a side view showing an electromagnetic waveirradiation unit in the apparatus for producing zeolite shown in FIG. 1.FIG. 3 is a schematic view showing an electromagnetic wave generator forthe electromagnetic wave irradiation unit shown in FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Following are explanations of an embodiment of the present inventionreferring to the drawings.

As shown in FIG. 1, incineration ash such as fly ash transported by atransportation vehicle or the like is stored in a raw material receivingvessel 1 and then sent to a preliminary heater 2 by a conveyer pump.Then an aqueous alkali at an alkali concentration of 1 to 30 percent byweight is added from an alkali storage tank 3. The mixture is heated to80 to 150° C., and then sent into a kneader 4 where the mixture iskneaded. The preliminary heater 2 is heated with steam 17, and thekneader 4 is operated by a motor 18.

A kneaded mixture 19 in the form of slurry formed in the kneader 4 isplaced on a conveyor 20 and conveyed to an electromagnetic waveirradiation unit 21. While the mixture is being conveyed, the mixture isirradiated with electromagnetic waves having a frequency of 2,450 MHzfrom electromagnetic wave irradiators 5 located over the conveyor 20 for1 to 15 minutes. In this way, the reaction for zeolite generationprogresses rapidly in the kneaded mixture 19, forming zeolite. It isnoted that the electromagnetic wave irradiation conditions can beadjusted in frequencies ranging from 300 MHz to 30 GHz (wavelength: 1cm-1 m) and in the irradiation time ranging from 1 to 30 minutes.

After completion of the electromagnetic wave irradiation, the kneadedmixture 19 is cured and then sent to a cleaning machine 7 where alkaliattached to the formed zeolite is washed off. Then, the cleaned zeoliteis dehydrated by a centrifuge 8 and mildly dried with steam heating in arotary steam dryer 9 to produce artificial zeolite. The artificialzeolite is put into a product receiving vessel 10, weighed to a specificweight value, packed, and shipped out as a product 16.

The aqueous alkali generated from the centrifuge 8 is sent to an alkalireceiving tank 11, treated in a primary waste water treatment apparatus12 and a secondary waste water treatment apparatus 13, passes through amonitoring apparatus 14, and then discharged as waste water 15.

In the electromagnetic wave irradiation unit 21, as shown in FIG. 2, afeed adjuster 22 for the kneaded mixture 19 is located in the proximityof the start of the conveyor 20, and a plurality of electromagnetic waveirradiators 5 are disposed over the conveyor 20. A curing floor 25 forthe formed zeolite is located in the proximity of the end of theconveyor 20, and a microwave prevention guide 26 is disposed inside theconveyor 20.

As shown in FIG. 3, adjacent to the microwave transmitter 23, disposedare an isolator 24 which prevents leak of the microwaves generated, adirectional coupler 27 for transmitting the generated microwaves to amicrowave irradiation section 32, a power monitor 28, an indicator 29, amatching device 30, a fixed distributor 31, and the microwaveirradiation section 32 for irradiating a materiel to be heated withmicrowaves, etc.

In the kneaded mixture 19 sent through the feed adjuster 22 and placedon the conveyor 20, reaction for zeolite generation rapidly progressesby irradiation with microwaves generated by the microwave transmitter 23while the kneaded mixture 19 is being conveyed and, therefore, zeoliteis formed in a short time until the mixture reaches the end of theconveyer 20. The zeolite thus formed is cured in the curing floor 25,and then sent, as described above, to the cleaning machine 7 in which aspecific treatment is performed.

Accordingly, in the course of adding an aqueous alkaline solution toincineration ash, kneading the resultant mixture, heating the kneadedmixture 19 thus formed, and irradiating the kneaded mixture 19 withelectromagnetic waves to form zeolite, a minimum amount of alkalinecessary for the reaction penetrates into the particle solid phase ofincineration ash, and the alkali instantly forms zeolite by means of theheat generated from inside the particles by the electromagnetic waveirradiation. This process, therefore, enables production of artificialzeolite in a short time, with a reduced amount of alkali used anddischarged. Further, the conventional solid-liquidseparation/purification processes are unnecessary, thereby simplifyingthe whole process.

Additionally, since the electromagnetic wave irradiation causes heatgeneration only in the kneaded mixture 19, virtually without heating thesurrounding devices, the atmospheric gases, etc., the heat efficiency ishigh and the energy consumption can be lessened. Furthermore, theelectromagnetic wave is irradiated after the kneaded mixture 19 ispreliminarily heated to approximately 80 to 150° C., thereby raising theheat conversion efficiency to approximately 70%.

The principal component of the zeolite formed by the embodiment of thepresent invention is phillipsite. It may also include faujasite, zeoliteA, hydroxy sodalite, etc. with non-zeolite components, that is,components other than zeolite, such as unburned carbon, iron, etc.

By irradiating the mixture with electromagnetic waves having a frequencyof 2,450 MHz, the dipole moments of water molecules existing in thekneaded mixture 19 vibrate vigorously (from several hundred million toseveral billion times per second) to give a high temperature bygenerating heat inside the particles of incineration ash or the like,which promotes a hot alkaline reaction instantly. Thus, the reaction toform zeolite, which took from several hours to several tens of hoursaccording to the conventional methods, can be completed in severalminutes.

Since the kneaded mixture 19 is in the form of slurry, the handling andtransportation efficiency in the production process are improved.Further, an efficient heat generation can be realized by theelectromagnetic wave irradiation. Thus, the amount of alkali can beadjusted to a minimum necessary for the reaction, resulting in greatreduction of the amount of discharged waste alkali.

It is noted that the present invention is not limited to theabove-described embodiment, and the components, concentrations andamounts of the aqueous alkali to be added can be varied according to thetype, components, properties, etc. of a raw material such asincineration ash. The water amount and the properties of the kneadedmixture, and the frequencies, the irradiation time, etc. of theelectromagnetic waves to be used in the irradiation can also be variedas appropriate.

EXAMPLE 1

A mixture of coal ash and incineration ash of sludge generated in papermanufacturing at a ratio of 1:2-5 was treated under the above-describedconditions using the apparatus for producing zeolite shown in FIG. 1.The conversion rate to Ca-type artificial zeolite was approximately 90%when the ratio was in the range of 1:2-3. It was possible to produce theCa-type artificial zeolite with high efficiency by the electromagneticwave irradiation for the duration of 3 to 5 minutes by accelerating theformation of zeolite nuclei through adding 10 to 20 percent by weight ofglass powder to the incineration ash of sludge generated in papermanufacturing.

EXAMPLE 2

Incineration ash from city garbage (RDF incineration ash) was treatedusing the apparatus for producing zeolite shown in FIG. 1. It waspossible to convert the incineration ash to zeolite in one half to onethird of the electromagnetic wave irradiation time compared with thecase of treating coal ash.

EXAMPLE 3

When treating a raw material having a different Si/Al ratio, such asincineration ash, etc., the components of the artificial zeolite formedcan be controlled by adjusting the ratio of Ca, Na, etc. which are thecomponents of the aqueous alkali to be added from the alkali storagetank 3, or by controlling the electromagnetic wave irradiation time.

Next, the method of manufacturing artificial zeolite according to thepresent embodiment was compared with the method of manufacturingartificial zeolite by means of the conventional hot aqueous alkalinesolution. In the method of the present embodiment, it was possible toreduce the pollution load to 5 kg per one ton of artificial zeolite fromthe conventional 100 kg and to reduce the energy consumption (heavyoil-converted) to 0.05 kl per one ton of artificial zeolite from 0.5 klwhich was necessary in the conventional method. Furthermore, it waspossible to reduce the production cost per one ton of artificial zeoliteto about 1/3.5 to 1/5 of the conventional cost.

Industrial Applicability

The present invention can be utilized as an efficient technology forproducing zeolite using incineration ash or a composition containingaluminosilicate, including natural zeolite, as a raw material.

What is claimed is:
 1. A method of producing zeolite comprising: addingan aqueous alkaline solution to incineration ash or a compositioncontaining aluminosilicate to form a mixture in the form of slurry ormud; heating said mixture; and directly irradiating said mixture withelectromagnetic waves having frequencies ranging from 300 MHz to 30 GHz,while continuously moving said mixture, thereby forming the zeolite. 2.The method of producing zeolite according to claim 1, wherein saidcomposition is natural zeolite or zeolite which has not been convertedinto phillipsite.